Fetching empty GCS storage bucket of type dir fails

[bobcatfish]

Expected Behavior

If a user is invoking a Task that needs a GCS bucket, sometimes that bucket will be empty and will be populated by the Task.

It should be possible to fetch this empty bucket and use it in the Task.

Actual Behavior

If you try to use a GCS storage resource with the dir flag set as an input, and the bucket is empty, the container which fetches the contents of the bucket fails with an error like:

Error executing command "gsutil cp -r gs://christies-empty-bucket/* /workspace/bucket" ; error exit status 1; cmd_output CommandException: No URLs matched: gs://christies-empty-bucket/*
"   
  stacktrace:  "main.main
	/Users/christiewilson/Code/go/src/github.com/tektoncd/pipeline/cmd/gsutil/main.go:94
runtime.main
	/usr/local/Cellar/go/1.10.3/libexec/src/runtime/proc.go:198"   
  ts:  1553120763.622061   

Steps to Reproduce the Problem

1. Make an empty GCS bucket (e.g. create a new one or delete everything from an existing one)
2. Crate a GCS bucket resource, e.g.:

---
apiVersion: tekton.dev/v1alpha1
kind: PipelineResource
metadata:
  name: tekton-bucket
spec:
  type: storage
  params:
   - name: type
     value: gcs
   - name: location
     value: gs://christies-empty-bucket # REPLACE with your own bucket
   - name: dir
     value: "y

3. Try to use that resource as an input to a task via a taskrun

Additional Info

In #632 we create a Task that operates on a bucket. If the bucket is empty, the intention is that it will create the folders it needs, and in subsequent calls it won't be empty.

[blrsn]

This seems to be an issue with gsutil. This is the same issue, but for rm command.
GoogleCloudPlatform/gsutil#417

gsutil fails for both
gsutil cp -r gs://empty-bucket /workspace/bucket
and
gsutil cp -r gs://empty-bucket/* /workspace/bucket